1. Field of the Invention
The present invention concerns an efficient method for preparing aromatic carboxylic acids, aromatic aldehydes, and aromatic alcohols, wherein the aromatic carboxylic acids, aromatic aldehydes, and aromatic alcohols are compounds represented by following formulae (II), (III), and (IV); ##STR2##
wherein n represents any of integer 1 to 5; and substituent R represents an alkyl group, an aryl group, an aralkyl group, halogen atom, haloalkyl group, OR.sup.1, SR.sup.1, SOR.sup.1, SO.sub.2, R.sup.2, NO.sup.2, NR.sup.1 R.sup.2, CH.sup.2 OR.sup.1, CH(OR.sup.1)(OR.sup.2), C(OR.sup.1)(OR.sup.2)(OR.sup.3), COR.sup.1, or COCOR.sup.1 wherein each of R.sup.1, R.sup.2, and R.sup.3 is selected from an alkyl group, an aryl group, and hydrogen atom; and when n is 2 or more, R may be the same or different.
The aromatic carboxylic acids, aromatic aldehydes, and aromatic alcohols are all regarded as industrially important raw materials for pharmaceutical and agricultural products, and polymer products.
2. Prior art
A reaction for producing the aromatic carboxylic acids from aromatic compounds having a methyl group, such as chlorotoluene, nitrotoluene, and the like, by oxidation, such as air oxidation, is a well known technique. Further, it is also well known that in said reaction an industrially important byproduct, such as aromatic aldehyde, aromatic alcohol, and etc., is produced.
In the oxidizing reaction, to effectively produce the aromatic carboxylic acid by suppressing formation of various intermediate oxidizing products, several approaches have been tried so far. For instance, a method for producing p-toluic acid by oxidation with a gas containing oxygen, in the presence of specific shaped catalyst of cobalt oxide (British Patent 1,005,315), a method for producing benzoic acid derivatives by liquid phase oxidation of toluene derivatives with a gas containing oxygen in the presence of a phase transfer catalyst composed of quaternary onium salt and transition metal salt, and together with a small amount of polar solvent, which is capable of dissolving said catalyst (Jp-A-1-2287054, "JP-A" used herein means unexamined Japanese Patent Publication), and the like, may be exemplified.
On the other hand, it is well known that aromatic carboxylic acids may be obtained by distilling, sedimenting with acid, or crystallizing reacting solution, or that aromatic aldehyde and aromatic alcohol may also be obtained by directly distilling the reacting solution, or by extracting an effective component from the reacting solution using an extracting solution, followed by rectifying thereof. (JP-B-48-23430, "JP-B" used herein means examined Japanese Patent Publication, JP-A-53-82734, JP-A-54-79244, JP-B-62-2576, JP-B-62-30974, JP-B-62-30975, JP-A-2-73038, JP-B-4-3370, JP-B-7-116096, and International Patent Publication 95-20560, and etc.)
Of the aromatic carboxylic acids, p-toluic acid may be produced by oxidizing p-xylene. As the byproduct of the reaction, p-methylbenzyl alcohol, p-tolualdehyde, p-hydroxymethylbenzoic acid, 4-carboxybenzaldehyde, terephthalic acid and the like, may be formed.
For purifying p-toluic acid produced the a physical process, such as distillation, extraction, and recrystallization, which are conventionally used, has not been applied, due to the sublimable nature of p-toluic acid, or its ready solubility in various solvents.
As a purifying process for p-toluic acid, a process has been known, which comprises treating at high temperature a crude p-toluic acid solution in organic an solvent, which is capable of selectively reacting in forming a salt of the byproducts, and removing the salt thus produced, in water extraction, and cooling the same (JP-A-54-79244). Subsequently, washing of the resulting crystals with n-hexane is carried out to further improve the purity of the p-toluic acid.
However, since an oxidizing reaction according to the conventional method is exclusively aimed at efficiently producing aromatic carboxylic acid from the aromatic hydrocarbons, regardless of the fact that some of the intermediates in the oxidation process, for example, aromatic aldehyde, and aromatic alcohol, are useful as raw material for pharmaceutical or agricultural products, the intermediates are disposed of as impurities, and are not efficiently utilized.
On the other hand, an attempt at effectively isolating whole compounds from the reacting solution containing these compounds, cannot be said as being sufficiently conducted. That is, since when an aromatic carboxylic acid is to be produced, all compounds other than the aromatic carboxylic acid, including aromatic aldehydes, and aromatic alcohols, are considered as impurities; a purification of the aromatic carboxylic acid only must be carried out. However, the aromatic aldehyde or aromatic alcohol is then reacted and decomposed, and is liable to be adversely affected in said purification of the aromatic acid. A similar phenomenon appears in the process for obtaining aromatic aldehydes and aromatic alcohols. As concrete examples, it is well known that if, generally, an aldehyde and alcohol are heated under acidic conditions, an acetal is formed with 1 moles of aldehyde and 2 mole of alcohol. Said reaction is the same phenomenon as those for purifying aromatic aldehydes and aromatic alcohols under distillation. By forming an acetal in the distillation, the yield of the aromatic aldehyde and aromatic alcohol may be reduced, resulting in lowering the yield, as well as purity. Thus, it is difficult to be capable of effectively obtaining all three of the compounds according to a combination of simple unit operations.
A among the aromatic carboxylic acids, p-toluic acid causes a significantly large loss of the product in washing operations, due to its solubility. In this connection, although p-methylbenzyl alcohol and p-tolualdehyde, which are byproducts, may form p-toluic acid by subsequent oxidation, these byproducts have never been recovered, nor utilized, so far.